Problem with flats

[Eddy Timmermans]

A few nights ago I made 180 frames of 60 seconds of Sadr in Cygnus.
Immediately after that, I took flats using the morning sky. I made sure the peak of the histogram was in the middle.
After that I made 30 darks.
I then put batch Preprocessing at work and after three hours of number crunching, a nice picture emerged.
However ther remained a few streaks and cirular patches, I thought would dissapear after applying the flats.
I checked a few flats and for some reason they were rotated 90° counterclockwise.
However, the master flat was correctly oriented.
I include the dropbox links to all files except bias.
Is there someone who can give me some advice or help ?
I think there is something wrong with the flats, but if I check individual lights aganst individual flats, the spots and streaks seem to match pretty good. So I'm in the dark here :-)
Thank you in advance for any hints.
Eddy

Light-binning : https://www.dropbox.com/s/dzhpybwa7y9twnm/light-BINNING_1.xisf?dl=0
Master Dark : https://www.dropbox.com/s/cawnf2smsl6dmof/dark-BINNING_1-EXPTIME_60.xisf?dl=0
Master Flat : https://www.dropbox.com/s/49h187u458qdrd6/flat-BINNING_1.xisf?dl=0

[Eddy Timmermans]

Some additional information :
I tried to stack fewer lights and flats while using the master dark en master bias, but that did'nt seem to help one bit.
It looked even worse.
So my guess is that the flats are not OK.
Would it help to rotate every single one 90° clockwise, and then try to stack them ?

Eddy